There is a saying "There lies a forest in every seed". We all have seen that after planting a seed, it grows up to be a plant, which then gives out fruits with many other seeds. Therefore, a forest can be grown from one seed if we kept on planting the new seeds that come out from it. It is indeed one of the evident miracles of Allah!
Similarly, the kalimah, there is no god but Allah and Muhammad is His messenger, is only one sentence in size but it contains the entire paradise in it. Success in this world, in the grave, on the Day of Judgement and hereafter lies only in obeying the message of this kalimah.